Download Frog Anatomy and Functions

Frog Anatomy and Functions
As members of the class Amphibia, frogs may live some of their adult lives on land, but
they must return to water to reproduce. Eggs are laid and fertilized in water. On the
outside of the frog’s head are two external nares, or nostrils; two tympani, or eardrums;
and two eyes, each of which has three lids. The third lid, called the nictitating
membrane, is transparent. Inside the mouth are two internal nares, or openings into the
nostrils; two vomerine teeth in the middle of the roof of the mouth; and two maxillary
teeth at the sides of the mouth. Also inside the mouth behind the tongue is the pharynx,
or throat. In the pharynx, there are several openings: one into the esophagus, the tube
into which food is swallowed; one into the glottis, through which air enters the larynx, or
voice box; and two into the Eustachian tubes, which connect the pharynx to the ear. The
digestive system consists of the organs of the digestive tract, or food tube, and the
digestive glands. From the esophagus, swallowed food moves into the stomach and then
into the small intestine. Bile is a digestive juice made by the liver and stored in the
gallbladder. Bile flows into a tube called the common bile duct, into which pancreatic
juice, a digestive juice from the pancreas, also flows. The contents of the common bile
duct flow into the small intestine, where most of the digestion and absorption of food into
the bloodstream takes place. Indigestible materials pass through the large intestine and
then into the cloaca, the common exit chamber of the digestive, excretory, and
reproductive systems. The respiratory system consists of the nostrils and the larynx,
which opens into two lungs, hollow sacs with thin walls. The walls of the lungs are filled
with capillaries, which are microscopic blood vessels through which materials pass into
and out of the blood. The circulatory system consists of the heart, blood vessels, and
blood. The heart has two receiving chambers, or atria, and one sending chamber, or
ventricle. Blood is carried to the heart in vessels called veins. Veins from different parts
of the body enter the right and left atria. Blood from both atria goes into the ventricle and
then is pumped into the arteries, which are blood vessels that carry blood away from the
heart. The urinary system consists of the frog’s kidneys, ureters, bladder, and cloaca. The
kidneys are organs that excrete urine. Connected to each kidney is a ureter, a tube
through which urine passes into the urinary bladder, a sac that stores urine until it
passes out of the body through the cloaca. The organs of the male reproductive system
are the testes, sperm ducts, and cloaca. Those of the female system are the ovaries,
oviducts, uteri, and cloaca. The testes produce sperm, or male sex cells, which move
through sperm ducts, tubes that carry sperm into the cloaca, from which the sperm move
outside the body. The ovaries produce eggs, or female sex cells, which move through
oviducts into the uteri, then through the cloaca outside the body. The central nervous
system of the frog consists of the brain, which is enclosed in the skull, and the spinal
cord, which is enclosed in the backbone. Nerves branch out from the spinal cord. The
frog’s skeletal and muscular systems consist of its framework of bones and joints, to
which nearly all the voluntary muscles of the body are attached. Voluntary muscles,
which are those over which the frog has control, occur in pairs of flexors and extensors.
When a flexor of a leg or other body part contracts, that part is bent. When the extensor
of that body part contracts, the part straightens.